Latex containing carboxymethyl dextran



United States Patent LATEX CONTAINING CARBOXYMETHYL nnxraAN Leo .LNovakand Elwood P. Wenzelberger, Dayton, Ohio, assignors, by mesneassignments, to Midland Chemical Corporation, Dayton, Ohio, acorporation of Delaware No Drawing. Application June 24, 1954 Serial No.439,152

2 Claims. (Cl. 260-17 .4)

This invention relates to stabilized natural or synthetic rubber latex.

Latex is an aqueous dispersion of natural or synthetic rubber. In thecase of the natural latex, proteins present therein as naturalimpurities function to some extent as stabilizers for the dispersion.However, in the case of both natural and synthetic latex it is desirableto include a protective stabilizing agent for the dispersion beforeshipping it to the ultimate user. A commonly used stabilizing andprotective agent is casein which is usually applied in solution inammonia, the latter being added to preserve the latex from putrefactionduring shipping and storage.

An object of this invention is to provide new stabilizing agents fornatural or synthetic rubber latex.

'Another object is to provide stabilizing and protective agents fornatural or synthetic rubber latex which also function to preserve thelatex from putrefaction during storage and shipping.

A further object is to provide agents which are efiective forstabilizing and protecting natural and synthetic latex in very smallamounts.

These and other objects of the invention which will become apparenthereinafter are accomplished by incorporating in the latex, natural orsynthetic, comparatively small amounts of carboxymethyl dextran.

The production of carboxymethyl dextran is described in the pendingapplication of L. J. Novak et al., Ser. No. 346,016, filed March 31,1953, now abandoned. In brief, the selected dextran and acarboxymethylating agent are reacted together in an aqueous alkalinemedium whereby the carboxymethyl group is substituted for one or morehydroxyl groups in the dextran molecule.

Suitable carboxymethylating agents are chloracetic acid, sodiumchloracetate or chloracetamide. The reaction is carried out in anaqueous solution of a strong alkali metal hydroxide such as sodium,potassium or lithium hydroxide. Preferably, the dextran is treated, inaqueous solution or suspension, with an excess of sodium or potassiumchloracetate in the presence of an excess of sodium or potassiumhydroxide at a temperature of 50 C. to 100 C. for ten minutes to twohours. Also preferably, the molar ratio of sodium chloracetate orpotassium chloracetate to dextran is between 2:1 and 12:1, the molarratio of sodium or potassium hydroxide to dextran is 5:1 to 15:1, andthe molar ratio of water to dextran is 70:1 to 120:1.

The carboxymethyl dextrans thus obtained have a D. S. (degree ofsubstitution or average number of carboxymethyl groups peranhydroglucopyranosidic unit) of less than 1:1 to 3:1.

The initial reaction product is a viscous mass comprising the sodium orpotassium salt of the carboxymethyl dextran, from which the salt may beprecipitated by a non-solvent therefor such as a water-miscible alcoholor ketone, e. g., methyl, ethyl, propyl, isopropyl or t-butyl alcohol oracetone.

The free ether may be recovered from the salt by mixing 2,856,372Patented Oct. 14, 1958.

2 the latter with water, acidifying, preferably to pH 2.0, andprecipitating the ether by means of a ketone or alcohol as mentionedabove. I

The dextran carboxymethylated may be obtained in various ways. Usually,it is biosynthesized from sucrose using microorganisms of theLeuconostoc mesenteroides or L. dextranicum types. Microorganisms (ortheir enzymes) which may be used include those bearing the followingNRRL (Northern Regional Research Laboratory) designations: Leuconostocmesenteroides B-S 12, B-119, B-1l46, 'B-1190, B-742, B-119l, B-ll96,B-1208, B-l216, B-1120, B-l144, B-523; St reptobacterium dextranicumB-l254 and Betabacterium vermiforme B-1l39.

The dextran is produced by introducing a'culture of the microorganism,or the enzyme filtered therefrom, into an aqueous sucrose-bearingnutrient medium and holding the mass until the dextran is synthesized inmaximum yield, after which it is precipitated by addition of awatermiscible aliphatic alcohol or ketone. The precipitated nativedextran is preferably purified and reduced to particulate condition forcarboxymethylation. This native dextran is normally characterized byvery high molecular weight, calculated to be in the millions. It may becarboxymethylated at the native molecular weight or it may be partiallyhydrolyzed to lower molecular weight in any suitable way, prior toreaction with the carboxymethylating agent. In general, the dextran mayhave a molecular weight of 5000 to 10 determined by light scatteringmeasurements, and may be a native dextran biosynthesized from sucroseunder specially controlled conditions such that the molecular weight islower than that of native dextran produced under conventionalconditions. i

Relatively small amounts of carboxymethyl dextran may be used inpracticing the invention. However, a preferred carboxymethyl dextran forthe present purposes is the ether derived from high molecular weightLeuconostac mesenteroids native, unhydrolyzed B-512 dextran (or anequivalent of that native dextran) and containing an average of 2.0 to3.0 carboxymethyl groups per A. G. U. This carboxymethyl dextran ispreferred because of its striking effectiveness in stabilizing the latexin small concentrations, such as amounts between 0.2% and 0.5% byweight.

The carboxymethyl dextran is incorporated by stirring it into the latexafter the latter has been prepared.

The rubber latex stabilized may be natural or synthetic rubber latex orconcentrated or creamed natural rubber latex, or pre-vulcanized rubberlatex. Further, the latex may be heat-sensitized by adding to itsuitable heat-unstable materials adapted to facilitate coagulation onheating. The invention is not limited to the stabilization of naturalrubber latex as other artificial latices such as formed by dispersingsynthetic rubbers in water may be treated. In these latter compositions,the carboxymethyl dextran may function as the stabilizing and protectiveagent and as dispersant for the rubber particles. The synthetic rubbermay comprise, for example, polymerized butadiene, isobutylene polymers,chloroprene polymers.

The usual rubber compound ingredients such as sulfur, zinc oxide;accelerators such as, for example, diphenyl guanidine, Pip-Pip(piperidine pentamethylene dithiocarbomate), Captax(mercaptobenzothiazole) and tetramethylthuriam disulfide; antioxidantssuch as Antox (condensation product of butyraldehyde-aniline), SantiflexB (reaction product of acetone and p-aminodiphenyl) and Agerite Alba(p-benzyloxy-phenol); lubricants such as stearic acid, Seriate (a kindof muscovite) and Aresplene (the sodium salt of an alkylated arylcompound marketed by Monsanto Chemical Co.); may be included in thelatex before, after, or simultaneously with conventional compoundingingredients or require changes in the manner in which the latex ishandled.

Thelatex may be vulcanized directly or after formation into a rubberarticle of desired shape. The articles may be formed by the well-knowndipping method with curing on the mold or form. Also, the stabilizedlatex may be formed into a rubber thread by the conventional procedureof extruding the stable latex through small orifices into a coagulatingand dehydrating bath, followed by washing, drying and vulcanizing of thethread in a continuous manner. The latex may also be used forimpregnating textiles, or it may be used to obtain spronge rubber bywhipping air into the stabilized latex containing, in addition to thecarboxymethyl' dextran, a dormant coagulant that becomes effective at acritical temperature and heating the whipped mass to complete thevulcanization. Dormant coagulants whichare representative include sodiumfluorosilicate, ammonium acetate, calcium formate and zinc ammoniumchloride.

Fillers may be included in the latex-carboxymethyl dextran mixture,useful fillers including those of the cellulosic type such as wood pulpor wood flour, as well as asbestos fibers, mineral wool, glass fibersand mineral pigments.

the precipitant to form in the shape of crumbs or granules.

For purposes of further description and of illustration only and not aslimitative, there are given the following examples of specificembodiments of the invention.

Example I About 5 parts by weight of carboxymethyl dextran derived fromL. m. B-S 12 high molecular weight native dextran and having a D. S. ofabout 2.8 are added to 200 parts by weight of 64.5 percent latex. Themixture is agitated until a creamy, homogeneous, stable mass results.

Instead of precipitating the stabilized latex as crumbs or granules byagitation of the latex with the coagulant,

, a comminuted of powdered product may be obtained by extruding, castingor otherwise shaping the latex containing the carboxymethyl dextran intoa layer, film, filament or rod, coagulating the latex in that form, andthereafter mechanically comminuting the shaped structure as by grinding,chopping or cutting.

Various changes and modifications may be made in details in practicingthe invention. Since such changes may be made within the disclosure andwithout departing from the spirit and scope of the invention, it is tobe understood that itis not intended to limit the invention except asdefined in the appended claims.

The term rubber latex? as used in the claims is intended to include bothnatural and synthetic latices.

tran and having a D. S. of about 2.8 and having admixed therewith 200parts of latex containing 64.5% rubber.

References Cited in the file of this patent UNITED STATES PATENTS2,518,135 Gaver Aug. 8, 1950 2,537,190 Lankan et a1 Jan. 9, 19512,602,082 Owen July 1, 1952 2,666,042 Nozaki Jan. 12, 1954 2,671,779Gaver Mar. 9, 1954

1. A COMPOSITION CONSISTING OF A CREAMY, HOMOGENEOUS MASS COMPOSED INPARTS BY WEIGHT OF 5 PARTS CARBOXYMETHYL DEXTRAN AND 200 PARTS OF LATEXCONTAINING 64.5% RUBBER.